The needs for higher processing speed and greater recording capacity are increasing among the magnetic disk apparatus (hereinafter collectively referred to as HDD) and other magnetic recording apparatus, and quite a number of efforts are being made for increasing the recording density. In order to meet the requirements for the higher density recording, the HDDs employ a thin film head, which head consisting of an inductive head for recording, and a magnetoresistive head (MR head), or a giant MR head (GMR head), for reproducing the signals.
A conventional thin film head is described below referring to FIG. 23 and FIG. 24. FIG. 23 is a perspective view showing outline at the sliding surface of a conventional thin film head facing a recording medium. FIG. 24 shows an outline view of the thin film head in the front.
In FIG. 23, a lower gap layer 232 of Al2O3, AlN, SiO2, or other nonmagnetic insulating material is formed on a lower magnetic shield layer 231 made of a soft magnetic material such as Permalloy, a Co amorphous magnetic layer, an Fe alloy magnetic layer. On the upper surface of the lower gap layer 232, a magnetoresistive element 233 (an MR element or a GMR element, hereinafter both are collectively referred to as GMR element) is deposited, and a transverse biasing layer 234 is formed by a CoPt alloy or other such magnetic material at both of the right and the left ends of the GMR element 233. A lead layer 235 of conductive material such as Cu, Cr, Ta, etc. is provided on the upper surface of the transverse biasing layer 234 so that the lead layer 235 makes contact with a ridge line formed by the upper surface of the GMR element 233 and the end face. The lead layer 235 may be disposed on the upper surface of the transverse biasing layer 234 so that it covers part of the upper surface of the GMR element 233. Next, an upper gap layer 236 is formed over the lead layer 235 and the exposed region of the GMR element 233, using the same nonmagnetic insulating material as the lower gap layer 232. Further on top of the upper gap layer 236, an upper magnetic shield layer 237 is provided using the same soft magnetic material as the lower magnetic shield layer 231. This completes the reproducing part 238 of magnetoresistive head.
On the upper surface of the upper magnetic shield layer 237, a recording gap layer 241 is formed using the same nonmagnetic insulating material as the lower gap layer 232. An upper magnetic core 242, which faces to the upper magnetic shield layer 237 via the recording gap layer 241 and makes contact with the upper magnetic shield layer 237 at the rear scene of FIG. 23, is provided in the form of a layer using a soft magnetic material. Between the upper magnetic shield layer 237 and the upper magnetic core 242 facing to each other with the interposing recording gap layer 241, a coil 243 is provided electrically isolated from both the upper magnetic shield layer 237 and the upper magnetic core 242. This completes the recording part 240 of a magnetoresistive thin film head. The upper magnetic shield layer 237 works as the shield for the reproducing part 238 and as the lower magnetic core of the recording part 240.
FIG. 24 shows outline view in the front of the reproducing part at the vicinity of magetoresistive element of the above-described thin film head. A lower gap layer 232 is provided on the upper surface of the lower magnetic shield layer 231. On the lower gap layer 232, an antiferromagnetic layer 244 formed of a magnetic material such as an FeMn alloy, a PtMn alloy, a pinned layer 245 formed of a magnetic material such as a NiFe alloy, Co, a CoFe alloy, a nonmagnetic conductive layer 246 formed of a nonmagnetic conductive material such as Cu, a free magnetic layer 247 formed of the same material as the pinned layer 245, and a cap layer 248 formed of a nonmagnetic material such as Ta, are deposited sequentially. The laminated body of stacked layers is defined at both the right and the left ends by ion-milling or the like method so that each of the cut ends has a slant surface. Thus a GMR element 233 is provided. A pair of transverse biasing layers 234 are formed at both ends of the GMR element 233 in physical contact with the slant end surfaces, and a pair of the right and the left lead layers 235 are provided on the transverse biasing layers 234. On top of them, an upper gap layer 236 is formed, followed by upper magnetic shield layer 237. Gap length 249 of the reproducing part 238, which represents a total sum in the thickness of the lower gap layer 232, the GMR element 133, and the upper gap layer 236, takes a very small value, so that it is capable of reproducing the short-wavelength signals of high density recording.
Recording current supplied to the coil 243 generates recording magnetic fields in the recording gap layer 241 disposed between the upper magnetic core 242 and the upper magnetic shield layer 237 of the recording head 240, for recording the signals on a magnetic recording medium. The reproducing head 238 detects signal magnetic fields from a magnetic recording medium storing the signals, and signals reproduced by the GMR element 233 in accordance with the resistance change are taken out through the terminal of lead layer 235.
In order to be able to reproduce the short-wavelength signals stored in a magnetic recording medium, gap length of a reproducing head needs to be sufficiently short. As described earlier, the gap length is a distance between the upper surface of the lower magnetic shield layer and the lower surface of the upper magnetic shield layer. It means that the distance is represented by a total thickness of lower gap layer, the GMR element, and the upper gap layer. The short distance means that a pair of transverse biasing layers disposed at both the right and the left ends of the GMR element are existing very close to the lower magnetic shield layer or the upper magnetic shield layer. Under such circumstance, magnetic fields of the transverse biasing layers easily escape to the lower magnetic shield layer or the upper magnetic shield layer. Thus in a thin film head of the conventional structure, the biasing magnetic field, applied to the free magnetic layer of GMR element, becomes weak. And the direction of magnetization of the free magnetic layer is not orientated in a stable manner, and the noise increases, making it difficult to obtain stable reproducing signals.